Silicone composition and a pressure sensitive adhesive film having a pressure sensitive adhesive layer made from the composition

ABSTRACT

A pressure sensitive adhesive film comprising a substrate film and a pressure sensitive adhesive layer formed on a surface of the substrate film, said pressure sensitive adhesive layer being prepared from (A) a silicone composition comprising a diorganopolysiloxane having at least two alkenyl groups per molecule and (C) a polyorganosiloxane having an SiH bond, characterized in that the alkenyl groups are contained in an amount of from 0.0007 to 0.05 mole per 100 g of the diorganopolysiloxane (A) and that the polyorganosiloxane (C) is contained in such an amount that a molar ratio of the SiH bond to the alkenyl group of the diorganopolysiloxane (A) ranges from 0.5 to 20.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/258,895,filed Oct. 27, 2005, the benefit of which is claimed under 35 U.S.C. §120. This application also claims benefit of Japanese Patent applicationNo. 2004-314694, filed on Oct. 28, 2004, and Japanese Patent applicationNo. 2005-311174, filed on Oct. 26, 2005. The contents of all of theforegoing applications are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a pressure sensitive adhesive film anda silicone composition to be used to form an adhesive layer of the film.The pressure sensitive adhesive film is suitable to apply on a surfaceof a flat panel display.

DESCRIPTION OF THE PRIOR ART

Flat panel displays are widely used as displays of electronic orelectric appliances. Examples of such displays include cathode ray tube(CRT) displays, liquid crystal displays, plasma displays, organicelectroluminescence displays, inorganic electroluminescence displays,light-emitting diode (LED) displays, Surface-Conduction Electron-emitterdisplays, Field Emission Displays, and touch panels using thesedisplays. To protect the displays from damage, dirt, fingerprints,electric charges, and strangers' glances, or to prevent glare orreflection, various kinds of films are applied to the displays.

These films, even when used for a display placed inside an electricappliance, should not entrap bubbles when they are applied on displaysand, if bubbles are entrapped, they should be removed easily. Theapplied film should not slide or peel on its own, but be easily peeledby hand when it is to be replaced with another film.

As a pressure sensitive adhesive layer of the film, a pressure sensitiveadhesive comprising an organic resin such as an acrylic resin and aurethane resin have been conventionally used. A film using such anadhesive composition, however, is difficult to stick without entrappingbubbles. When bubbles are entrapped, they cause unevenness in luminance,brightness and color in a display, so that the film should be peeled andre-stuck or the bubbles should be push out with fingers. Thesere-sticking of the film and pushing out sometimes damage the display.

Japanese Patent Application Laid-Open No. 2004-225005 discloses asolvent free organopolysiloxane composition. A pressure sensitiveadhesive layer prepared by curing the composition does not havesufficient adhesion strength, so that the adhesive layer sometimes peelsoff from the substrate. This peeling cannot be prevented completely bytreating the substrate with corona discharge or a primer. Further, anapplied composition is sometimes strongly electrostatically charged toflow on the substrate before cured, resulting in an adhesive layerhaving an uneven thickness.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a pressure sensitivefilm suitable for a flat panel display which film can be applied on adisplay without entrapping bubbles and, after applied, does not slide orpeel on its own but can be easily peeled by hand. Another object of thepresent invention is to provide a composition for a pressure sensitiveadhesive of the film. After extensive studies, the inventors have foundthat the foregoing objects can be attained by a silicone compositionhaving a specific degree of curability.

Thus, the present invention is a pressure sensitive adhesive filmcomprising a substrate film and a pressure sensitive adhesive layerformed on a surface of the substrate film, said pressure sensitiveadhesive layer being prepared from (A) a silicone composition comprisinga diorganopolysiloxane having at least two alkenyl groups per moleculeand (C) a polyorganosiloxane having an SiH bond, characterized in thatthe alkenyl groups are contained in an amount of from 0.0007 to 0.05mole per 100 g of the diorganopolysiloxane (A) and that thepolyorganosiloxane (C) is contained in such an amount that a molar ratioof the SiH bond to the alkenyl group of the diorganopolysiloxane (A)ranges from 0.5 to 20.

The aforesaid present film can be applied on an object withoutentrapping bubbles. The applied film well sticks to the object withoutsliding or peeling. The film can be peeled off easily by hand.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present composition, component (A) is a polydiorganosiloxanehaving at least two alkenyl groups per molecule. Examples of suchpolydiorganosiloxane are represented by any one of the followingformulae,

wherein, R² is a substituted or unsubstituted monovalent hydrocarbongroup which does not have an aliphatic unsaturated bond; R³ is anorganic group having an alkenyl group; a is an integer of from 0 to 3,preferably 1; m is an integer of 0 or larger, provided that m is 2 orlarger when a is zero; n is an integer of 10 or larger, with a sum of mand n being such that the polydiorganosiloxane has a viscosity of 10mPa·s or larger.

Preferably, R² has 1 to 10 carbon atoms. Examples of R² include alkylgroups such as methyl, ethyl, propyl, and butyl groups; alicyclic groupsuch as cyclohexyl group; aryl groups such as phenyl and tolyl groups.R² may have a substituent group such as a halogen, amino, hydroxyl, orcyano group to be, for example, 3-aminopropyl group,3,3,3-trifluoropropyl group, 3-hydroxypropyl group or 3-cyanopropylgroup. Preferred R² are methyl and phenyl groups.

R³ preferably has 2 to 10 carbon atoms. Examples of R³ include vinyl,allyl, hexenyl, octenyl, acryloylpropyl group, acryloylmethyl group,methacryloylpropyl group, cyclohexenylethyl group, and vinyloxypropylgroup, among which a vinyl group is preferred from industrial viewpoint.In the present composition, component (A) is characterized in that itcontains alkenyl groups in an amount of from 0.0007 to 0.05 mole per 100g of component (A). Within the range, a suitable adhesive strength bothto a surface of a flat panel display and a substrate film can beattained. When a mass ratio of Component (A) to Component (B) is in therange of from 55/45 to 40/60, Component (A) preferably has alkenylgroups in an amount of from 0.005 to 0.05 mole/100 g.

The polydiorganosiloxane (A) may preferably be oily or gummy. Oilycomponent (A) preferably has a viscosity at 25° C. of 10 mPa·s orhigher, particularly 100 mPa·s or higher. If the viscosity is below theaforesaid lower limit, a composition may not be hardened enough, orcohesive strength may be too small. When component (A) is gummy, aviscosity of a 30 wt % solution of it in toluene is preferably 100,000mPa·s or lower. If the viscosity exceeds the aforesaid upper limit, acomposition may be so viscous that the composition is difficult to beagitated in its preparation process. The component (A) may be a mixtureof two or more kinds of the polydiorganosiloxane.

Typically, the polydiorganosiloxane (A) is prepared by subjecting cyclicmonomers such as octamethylcyclotetrasiloxane to a ring-openingpolymerization. The polymerization product is preferably purified byheating at a reduced pressure while passing inert gas in the product toremove low molecular weight cyclic siloxanes.

Component (B) is a polyorganosiloxane comprising a R¹ ₃SiO_(0.5) unitand a SiO₂ unit in a molar ratio of R¹ ₃SiO_(0.5) unit to SiO₂ unit offrom 0.6 to 1.7. If the ratio is below the aforesaid lower limit,adhesion strength or tackiness may be lower. If the ratio exceeds theaforesaid upper limit, adhesion strength and holding power may be lower.

R¹ is a substituted or unsubstituted monovalent hydrocarbon group having1 to 10 carbon atoms. Examples of R¹ include alkyl groups such asmethyl, ethyl, propyl, and butyl groups; alicyclic groups, phenyl group,a vinyl group, an allyl group and a hexenyl group. R¹ may have asubstituent group such as a halogen, amino, hydroxyl, or cyano group tobe, for example, 3-aminopropyl group, 3,3,3-trifluoropropyl group,3-hydroxypropyl group or 3-cyanopropyl group.

Component (B) may have an OH-group in an amount of from 0.01 to 4.0 wt %based on a total weight of component (B). If the amount is below theaforesaid lower limit, cohesive strength of a composition may be toolow. If the amount exceeds the upper limit, tackiness of a curedcomposition may be too small.

Component (B) may be a mixture of two or more of the polyorganosiloxane.Component (B) may also have R¹SiO_(1.5) unit and R¹ ₂SiO unit in suchamounts that they do not adversely affect properties of the presentcomposition.

A mass ratio of Component (A) to Component (B), (A)/(B), ranges from95/5 to 40/60, preferably from 95/5 to 55/45. A composition with theratio being below the aforesaid lower limit may give a film whichentraps many bubbles when it is applied on an object and may bedifficult to peel due to too large adhesion strength.

Component (C) is an organohydrogenpolysiloxane crosslinking agent havingat least 2, preferably at least 3, hydrogen atoms bonded to siliconatoms and may be linear, branched or cyclic siloxane.

Examples of component (C) are as shown below, but not limited thereto.

In the above formulae, each R² may be the same or different from otherR² and is a substituted or unsubstituted monovalent hydrocarbon grouphaving no aliphatic unsaturated group; b is 0 or 1; p and q each is aninteger of 0 or larger, provided that p is 2 or larger when b is 0, anda sum of p and q is such that the organohydrogenpolysiloxane has aviscosity of from 1 to 5,000 mPa·s at 25° C.; s is an integer of 2 orlarger, t is an integer of 0 or larger with s+t≧3, preferably 8≧s+t≧3.

Examples of R² include alkyl groups such as methyl, ethyl, propyl, andbutyl groups; alicyclic group such as cyclohexyl group; aryl groups suchas phenyl and tolyl groups. R² may have a substituent group such as ahalogen, amino, hydroxyl, or cyano group to be, for example,3-aminopropyl group, 3,3,3-trifluoropropyl group, 3-hydroxypropyl groupor 3-cyanopropyl group. Preferred R² are methyl and phenyl groups.

Preferably, a viscosity at 25° C. of the organohydrogenpolysiloxane (C)ranges from 1 to 5,000 mPa·s, more preferably from 5 to 500 mPa·s.Component (C) may be a mixture of two or more of theorganohydrogenpolysiloxane.

Component (C) may be used in such an amount that a molar ratio of theSiH bond in component (C) to the alkenyl group of component (A) rangesfrom 0.5 to 20, preferably from 0.8 to 15. If the ratio is below theaforesaid lower limit, crosslinking density may be too low to givesufficient cohesive strength or holding power. If the ratio exceeds theaforesaid upper limit, crosslinking density may be too high to attainappropriate adhesion strength and tackiness.

Component (D) is a retarder which prevents the adhesive composition frombecoming thicker or from gelling during the preparation of thecomposition or before heat curing the composition applied on asubstrate. Examples of component (F) include 3-methyl-1-butyn-3-ol,3-methyl-1-pentyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 1-etynylcyclohexanol,3-methyl-3-trimethylsiloxy-1-butyn, 3-methyl-3-trimethylsiloxy-1-pentyn,3,5-dimethyl-3-trimethylsiloxy-1-hexyn, 1-ethynyl-1-trimethysiloxycyclohexane, bis(2,2-dimethyl-3-butynoxy)dimethyl silane,1,3,5,7-tetramethyl-1,3,5,7-tetravinyl cyclotetrasiloxane, and1,1,3,3-tetramethyl-1,3-divinyl disiloxane.

Preferably, component (D) is incorporated in the composition in anamount, based on a total of components (A) and (B) of 100 parts byweight, of from 0 to 8.0 parts by weight, more preferably 0.05 to 2.0parts by weight. If the amount exceeds the aforesaid upper limit, thecomposition may not be cured enough.

Component (E) is a catalyst for an addition reaction. Examples of thecatalyst (E) include chloroplatinic acid, alcohol solutions ofchloroplatinic acid, reaction products of chloroplatinic acid withalcohols, reaction products of chloroplatinic acid with olefincompounds, and reaction products of chloroplatinic acid with siloxanehaving a vinyl group, a platinum-olefin complex, a complex of platinumwith a siloxane having a vinyl group, rhodium complexes, and rutheniumcomplexes. These may be in the form of a liquid dissolved or dispersedin a solvent such as isopropanol and toluene, or in a silicone oil.

Component (E) is incorporated in the composition preferably in such anamount that the amount as noble metal ranges from 5 to 2,000 ppm,particularly from 10 to 500 ppm. If the amount is below the aforesaidlower limit, insufficient curing and lower crosslinking density mayoccur, resulting in too small holding power. If the amount exceeds theaforesaid upper limit, a serviceable time of the composition may beshorter.

Examples of organic solvent (F) include aromatic hydrocarbon solventssuch as toluene and xylene; aliphatic hydrocarbon solvents such ashexane, heptane, octane, isooctane, decane, cyclohexane,methylcyclohexane, and isoparaffin; hydrocarbon solvents such asindustrial gasoline, petroleum benzene, and solvent naphtha; ketonesolvents such as acetone, methylethylketone, 2-pentanone, 3-pentanone,2-hexanone, 2-heptanone, 4-heptanone, methylisobutylketone,diisobutylketone, acetonylacetone, an cyclohexanone; ester solvents suchas ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, andisobutyl acetate; ether solvents such as diethyl ether, dipropyl ether,diisopropyl ether, dibutyl ether, 1,2-dimethoxyethane, and 1,4-dioxane;solvents having both ester and ether moieties such as 2-methoxyethylacetate, 2-ethoxyethyl acetate, propylene glycol monomethyl etheracetate, 2-butoxyethyl acetate; silicone solvents such ashexamethyldisiloxane, octamethyltrisiloxane,octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane,tris(trimethylsiloxy)methylsilane, and tetraquis(trimethylsiloxy)silane;and a mixture thereof.

Preferred are aliphatic hydrocarbon solvents such as hexane, heptane,octane, isooctane, decane, cyclohexane, methylcyclohexane, andisoparaffin. Also preferred is a mixture of the aliphatic hydrocarbonsolvent with an ether solvent, an ester solvent, or a solvent havingboth ester and ether moieties.

The present composition can be prepared by mixing components (A), (B),(C), (D), and (F). To prepare the present film, the composition may befurther diluted with an organic solvent, if needed, to which component(E) is added and mixed, and then applied to a substrate film of variouskinds as described below.

A part or all of the components (A) and (B) may be added as a productprepared by reacting the part or all of the components (A) and (B) inthe presence of a basic catalyst and a part or all of the component (F),if needed, to remove residual hydroxyl groups in the components byetherification.

Examples of the basic catalyst include metal hydroxides such as lithiumhydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide;carbonates such as sodium carbonate and potassium carbonate;bicarbonates such as sodium bicarbonate; organic metals such as sodiummethoxide, potassium buthoxide and butyl lithium; a complex of potassiumhydroxide with a polysiloxane; nitrogen compounds such as ammonium gas,ammonia water, methyl amine, trimethylamine, and triethylamine.Preferred are ammonia gas and ammonia water. The reaction may be carriedout at a temperature of from 20 to 150° C. Typically, a temperature offrom room temperature to a reflux temperature of component (F) isemployed. The reaction time may range from 0.5 to 10 hours, preferablyfrom 1 to 6 hours.

After the reaction, a neutralizing agent may be added to neutralize thebasic catalyst, if needed. Examples of the neutralizing agent includeacidic gases such as hydrogen chloride and carbon dioxide; organic acidssuch as acetic acid, n-octylic acid and citric acid; and mineral acidssuch as hydrochloric acid, sulfuric acid, and phosphoric acid.

In addition to the above components, the present silicone adhesivecomposition may comprise optional components. Examples of suchcomponents include non-reactive polyorganosiloxanes having no alkenylgroup such as polydimethylsiloxane and polydimethyldiphenylsiloxane;antioxidants such as phenol type, quinone type, amine type, phosphorustype, phosphite type, sulfur type, and thioether type antioxidants;photostabilizers such as triazole type and benzophenone typephotostabilizers; flame retardants such as phosphate ester type, halogentype, phosphorus type, and antimony type flame retardants; antistaticagents such as cationic surfactants, anionic surfactants, and nonionicsurfactants; solvents for lowering the viscosity in application, forexample, aromatic solvents such as toluene and xylene, aliphaticsolvents such as hexane, octane and isoparaffins, ketones such as methylethyl ketone and methyl isobutyl ketone, esters such as ethyl acetateand isobutyl acetate, and ethers such as diisopropyl ether and1,4-dioxane; and mixtures thereof; and dyes and pigments.

An adhesive layer prepared from the present silicone composition showsadhesion strength to a stainless steel plate measured according to a180-degree peel test specified in the Japanese Industrial Standards Z0237, using an adhesive film having 30 μm-thick adhesive layer on 25μm-thick polyethylene terephthalate substrate film. Preferably, theadhesion strength ranges from 0.01 to 2.5N/10 mm, more preferably from0.01 to 1.5 N/10 mm, and most preferably from 0.1 to 0.5 N/10 mm. Anadhesive layer having the strength below the aforesaid lower limit maynot stick to a display surface. A film having the strength above theaforesaid upper limit may not be easy to peel by hand.

The present silicone composition for a pressure sensitive adhesive canbe applied on various substrates and cured to form a pressure sensitiveadhesive layer.

Examples of the substrate film include films of plastic such aspolyester, poly(meth)acrylate, polycarbonate, polyethylene,polypropylene, polystyrene, polyamide, polyimide, polyphenylene sulfide,polytetrafluoroethylene, polyvinylchloride, polyurethane,triacetylcellulose, polyacetal, polynorbornene sold under the trade nameof Arton from JSR Co., cycloolefinic resin sold under the trade name ofZEONOR from ZEON Co., epoxy resin, and phenolic resin, and a laminatedfilm comprising a plurality of these films. Preferably, polyester suchas polyethylene terephthalate, polybutylene terephthalate, andpolyethylene naphthalate, poly(meth)acrylate, and polycarbonate areused.

A thickness of the substrate film may be selected depending on plastic,but typically ranges from 10 to 300 μm, more typically from 20 to 200μm.

To improve adhesion between the substrate and the pressure sensitiveadhesive layer, the substrate may be subjected to primer coatingtreatment, corona treatment, etching plasma treatment or sand blasttreatment. Preferably, the substrate film is treated with coronadischarge and then with a primer coating.

Primer compositions which can be used in the present invention include acondensation type composition comprising a polydiorganosiloxane havingSiOH groups at both ends, a polysiloxane having a SiH group and/or apolysiloxane having an alkoxy group, and a condensation catalyst; and anaddition type composition comprising a polydiorganosiloxane having analkenyl groups such as a vinyl group and a polysiloxane having a SiHgroup and an addition catalyst.

An example of the condensation type primer composition is described inJapanese Patent Publication No. S54-44017, which composition comprises apolydiorganosiloxane having a hydroxyl groups at an end, anorganohydrogenpolysiloxane, and a tin salt of an organic carboxylicacid.

Another example of the condensation type primer composition is describedin Japanese Patent Publication No. S54-44017, which compositioncomprises an organopolysiloxane (a) represented by the following generalformula,

wherein R is a substituted or unsubstituted monovalent hydrocarbon groupand n is an integer of 30 or larger, an organohydrogenpolysiloxane (b)having at least three SiH bonds and a substituted or unsubstitutedmonovalent hydrocarbon group, a vinylic and/or an acrylic copolymer (c)having a hydrolyzable silyl group and a metal salt of an organiccarboxylic acid (e).

An example of the addition type silicone primer composition is describedin Japanese Patent Publication S60-11950, which composition comprises anorganopolysiloxane having a vinyl group, an organohydrogenpolysiloxane,and a platinum catalyst.

Another example of the primer composition is described in JapanesePatent Application Laid-Open No. 2002-338890, which compositioncomprises a diorganopolysiloxane (A) having alkenyl group at both endsand an average degree or polymerization of from 500 to 2000, saidalkenyl group being present in a molar concentration of from 0.001 to0.005 mole per 100 g of the diorganopolysiloxane, anorganohydrogenpolysiloxane (B) having at least two SiH bonds, a platinumcatalyst (C), and a retarder (D).

Still another example of the primer composition is described in JapanesePatent Application Laid-Open No. 2004-307653, a diorganopolysiloxane (A)having alkenyl group at both ends and a phenyl group in an amount offrom 0.5 to 60 mole %, an organohydrogenpolysiloxane (3) having at leasttwo SiH bonds, a platinum catalyst (C), and a retarder (D).

In the present invention, both type of the primer composition may beused.

A film surface opposite to the surface on which an adhesive layer isprovided is preferably treated to be damage-proof, dirt-proof,fingerprints-proof, anti-glare, anti-reflection or antistatic. Thetreatment can be performed before or after the adhesive layer isprovided.

Examples of the damage-proof treatment agent, i.e., hard coat treatment,include acrylate, silicone, oxycetane, inorganic materials, and organichybrid materials hard coating agents.

Examples of the dirt-proof treatment agent include fluorinated,silicone, ceramic, and photocatalyst dirt-proof treatment agents.

Examples of the anti-glare treatment include wet treatment by applying afluorinated or a silicone anti-glare agent and dry treatment by vapordeposition or sputtering.

Examples of the antistatic agent include surfactants, silicones,organoborons, electroconductive polymers, metal oxides, metal vapors.

To apply the composition, any known means or method for application maybe used, for example, a comma coater, a lip coater, a roll coater, a diecoater, a knife coater, a blade coater, a rod coater, a kiss-rollcoater, and a gravure coater; screen printing, dipping and castingmethods.

The amount of the composition to be applied on a substrate may be suchthat a cured adhesive layer has a thickness of from 2 to 200 μm,particularly from 3 to 100 μm.

Curing may be carried out at a temperature of from 80 to 130° C. for 30seconds to 3 minutes.

The adhesive tape can be prepared by applying the silicone compositionon the substrate film as described above, or by applying the compositionon a release film or a release paper having been coated with a releasingagent, curing the composition and then transferring the curedcomposition to the aforesaid substrate film. A peelable protective filmmay be applied on the present pressure sensitive adhesive layer, ifnecessary, to protect the layer during storage or transportation.

The film prepared by using the present pressure sensitive adhesivesilicone composition are used for flat panel displays for displayingletters, symbols, and images of various apparatuses, such as TVmonitors, computer monitors, handheld terminal monitors, surveillancemonitors, video cameras, digital cameras, cell phones, instrumentalpanel displays of automobiles, various facilities, instruments, andtools, automatic ticket vending machine, and automated teller machine.Examples include displays such as CRT displays, liquid crystal displays,plasma displays, organic electroluminescence displays, inorganicelectroluminescence displays, LED displays, Surface-ConductionElectron-emitter displays, Field Emission Display and touch panels usingthese displays.

The present film is used to protect these displays from damages, dirt,fingerprints, electric charges, or strangers' glances or to preventrefection on the displays.

EXAMPLES

The present invention will be explained with reference to the followingExamples, but not limited thereto. The term “parts” means parts byweight, “Me” means a methyl group, “Vi” means a vinyl group, and “Ph”means a phenyl group.

I. Test Methods

The following test methods were used.

Adhesion Strength

A pressure sensitive adhesive film was prepared by applying a solutionof a silicone adhesive composition on a 25 μm thick polyethyleneterephthalate film with an applicator in such a thickness that a curedadhesive layer at 120° C. for 1 minute has a thickness of 30 μm. A 10 mmwide tape sliced from the film was tested according to the 180-degreepeel test specified in the Japanese Industrial Standards Z 0237 asfollows.

The tape was attached to a stainless steel plate and pressed onto thestainless steel plate by rolling a rubber-lined roller of 2 kg in weightback and forth in two cycles on the tape. After leaving the stainlesssteel plate with the tape thereon at room temperature for about 20hours, a force in N/10 mm required to peel the tape off from the steelplate in 180 degrees by pulling at a speed of 300 mm/minute was measuredusing a tensile tester.

Holding Power

A pressure sensitive adhesive tape was prepared as in the adhesionstrength test. A tape of about 75 mm in length and 25 mm in width wasattached in an area of 25 by 25 mm on a lower end of a vertically heldstainless steel plate. At the lower end of the tape, a weight of 1 kgwas hung. After leaving the plate at 150° C. for 1 hour, a displacementof the position of the upper end of the tape before and after this 1hour was measured with a microscope.

Bubble Entrapment

The silicone primer composition was applied on a corona-treated surfaceof 75 μm thick polyethylene terephthalate film one surface of which hasbeen treated with corona. The primer composition was applied in such anamount that 0.5 g/m² of the composition was remain after cured at 120°C. for 30 seconds. On the primer layer, a silicone composition for apressure sensitive adhesive was applied with an applicator in such anamount that a thickness after cured is 30 μm. The applied compositionwas cured 120° C. for 1 minute to prepare a pressure sensitive adhesivefilm. From the film, a film of 10 cm width by 20 cm length was cut outand stuck on a glass plate at the shorter edge and then along the longeredge. During sticking the film, it was visually observed whether thefilm entrapped bubbles or not and was rated according to the followingcriteria.

A: No bubble was entrapped to allow very good sticking.

B: Some bubbles were entrapped but could be easily removed by pushing ona film with a finger.

C: Bubbles were entrapped and could no be push out.

Peelability

The film applied on the glass plate as in the bubble entrapment test waspeeled off from the glass plate by hand. Peelability was rated accordingto the following criteria.

A: A film was easily peeled by hand without fold or deformation andthere was no adhesive left on a glass plate.

B: A film could be peeled by hand but folded or deformed and there wasno adhesive left on a glass plate.

C: A film could be peeled by hand but folded or deformed and a part ofan adhesive was left on a glass plate

Adhesion Strength to a Substrate Film

An adhesive layer of a film prepared as in the bubble entrapment testwas scrubbed with a finger cushion and observed whether it was peeledoff or not. In the table 1, each rating means as follows.

A: An adhesive layer was not peeled.

B: An adhesive layer was partly peeled.

C: A whole adhesive layer was peeled.

II Corona Treatment, Primer Treatment

In the examples and comparative examples, substrate films were coronatreated and then treated with a primer, unless otherwise specified. Forthe primer treatment, a condensation type silicone primer composition,KR-3006A/CAT-PS-1, ex Shin-Etsu Chemical Co., Ltd., was used whichcomposition comprises a diorganopolysiloxane, KE76S, ex Shin-EtsuChemical Co., Ltd., an organohydrogenpolysiloxane, KF-99, ex Shin-EtsuChemical Co., Ltd., and dibutyl tin diacetate, CAT-PS-1, as condensationreaction catalyst.

Example 1-1

Mixed were 90 parts of a polydimethylsiloxane of the following formula,herein after referred to as “polydimethylsiloxane A1”, having a vinylgroup in an amount of 0.002 mole/100 g and a viscosity in a 30% solutionin toluene of 5,000 mPa·s,

wherein x=3,800, y=4 and z=0, 16.7 parts of a 60% solution in toluene ofpolysiloxane, herein after referred to as “polysiloxane B”, comprisingMe₃SiO_(0.5) unit and SiO₂ unit with a ratio of Me₃SiO_(0.5) unit/SiO₂unit being 0.85, and 60 parts of toluene.

To 100 parts of the mixture thus obtained, 0.35 part of apolyorganosiloxane having SiH

bonds of the following formula, herein after referred to as“polyorganosiloxane C1”, and 0.20 part of ethynylcyclohexanol were addedand mixed.

To 100 parts of the mixture containing 60 wt % of siloxanes, 50 parts oftoluene, and 0.5 part of a solution of a platinum complex with asiloxane having a vinyl group having a concentration as platinum of 0.05wt % in toluene, herein after referred to as “the platinum complexsolution”, were added. The silicone composition for pressure sensitiveadhesive thus obtained were evaluated according to the aforesaid testmethods.

Referential Example 1

The silicone composition prepared in Example 1 above was applied on a 75μm thick polyethylene film which was not corona-treated norprimer-treated. The adhesive film thus obtained was subjected tomeasurement of the adhesion strength to a substrate.

Referential Example 2

The silicone composition prepared in Example 1 was applied on a 75 μmthick polyethylene film which was corona-treated but not primer-treated.The adhesive film thus obtained was subjected to measurement of theadhesion strength to a substrate.

Example 1-2

The silicone composition prepared in Example 1 was applied on a 75 μmthick polyethylene film which was not corona-treated but primer-treated.The adhesive film thus obtained was evaluated according to the aforesaidtest methods.

Example 2

A solution was prepared by mixing 70 parts of a polydimethylsiloxane ofthe following formula, herein after referred to as “polydimethylsiloxaneA2”, having a vinyl group in an amount of 0.002 mole/100 g and aviscosity in a 30% solution in toluene of 16,000 mPa·s,

wherein x=6,600, y=8 and z=0, 50 parts of a 60% solution of thepolysiloxane B in toluene, and 46.7 parts of toluene, to which 0.5 partof 28% solution of ammonium in water was added and mixed at roomtemperature for 6 hours.

Then, the mixture obtained was heated under reflux for 4 hours toremoved ammonia gas and water. After cooled, fresh toluene was added tocompensate for distilled off toluene. To 100 parts of the product thusobtained, 0.27 part of the polyorganosiloxane C1, and 0.20 part ofethynylcyclohexanol were added and mixed.

To 100 parts of the mixture obtained containing about 60 wt % ofsiloxanes, 50 parts of toluene, and 0.5 part of the platinum complexsolution were further added to prepare a silicone composition containingabout 40 wt % of siloxanes. The silicone composition for pressuresensitive adhesive thus obtained was evaluated according to theaforesaid test methods.

Example 3

A solution was prepared by mixing 70 parts of a polydimethylsiloxane ofthe following formula, herein after referred to as “polydimethylsiloxaneA3”, having a vinyl group in an amount of 0.002 mole/100 g and aviscosity in a 30% solution in toluene of 15,000 mPa·s,

wherein x=4,500, y=7 and z=500, 50 parts of a 60% solution of thepolysiloxane B in toluene, and 46.7 parts of toluene, to which 0.5 partof 28% solution of ammonium in water was added and mixed at roomtemperature for 6 hours.

Then, the mixture was heated under reflux for 4 hours to removed ammoniagas and water. After cooled, fresh toluene was added to compensate fordistilled off toluene. To 100 parts of the reaction product thusobtained, 0.27 part of the polyorganosiloxane C1, and 0.20 part ofethynylcyclohexanol were added and mixed.

To 100 parts of the mixture obtained containing about 60 wt % ofsiloxanes, 50 parts of toluene, and 0.5 part of the platinum complexsolution were further added to prepare a silicone composition containingabout 40 wt % of siloxanes. The silicone composition for pressuresensitive adhesive thus obtained was evaluated according to theaforesaid test methods.

Example 4

A solution was prepared by mixing 75 parts of a polydimethylsiloxane ofthe following formula, herein after referred to as “polydimethylsiloxaneA4”, having a vinyl group in an amount of 0.04 mole/100 g and aviscosity in a 30% solution in toluene of 12,000 mPa·s,

wherein x=5,630, y=170 and z=0, 41.7 parts of a 60% solution of thepolysiloxane B in toluene, and 50 parts of toluene, to which 0.5 part of28% solution of ammonium in water was added and mixed at roomtemperature for 6 hours.

Then, the mixture was heated under reflux for 4 hours to removed ammoniagas and water. After cooled, fresh toluene was added to compensate fordistilled off toluene. To 100 parts of the reaction product thusobtained, 2.31 parts of the polyorganosiloxane C1, and 0.20 part ofethynylcyclohexanol were added and mixed.

To 100 parts of the mixture obtained containing about 60 wt % ofsiloxanes, 50 parts of toluene, and 0.5 part of the platinum complexsolution were further added to prepare a silicone composition containingabout 40 wt % of siloxanes. The silicone composition for pressuresensitive adhesive thus obtained was evaluated according to theaforesaid test methods.

Example 5

A solution was prepared by mixing 50 parts of a polydimethylsiloxane ofthe following formula, herein after referred to as “polydimethylsiloxaneA5”, having a vinyl group in an amount of 0.04 mole/100 g and aviscosity in a 30% solution in toluene of 23,000 mPa·s,

wherein x=7,760, y=240 and z=0, 83.3 parts of a 60% solution of thepolysiloxane B in toluene, and 33.4 parts of toluene, to which 0.5 partof 28% solution of ammonium in water was added and mixed at roomtemperature for 6 hours.

Then, the mixture was heated under reflux for 4 hours to removed ammoniagas and water. After cooled, fresh toluene was added to compensate fordistilled off toluene. To 100 parts of the reaction product thusobtained, 1.54 parts of the polyorganosiloxane C1, and 0.20 part ofethynylcyclohexanol were added and mixed.

To 100 parts of the mixture obtained containing about 60 wt % ofsiloxanes, 50 parts of toluene, and 0.5 part of the platinum complexsolution were further added to prepare a silicone composition containingabout 40 wt % of siloxanes. The silicone composition for pressuresensitive adhesive thus obtained was evaluated according to theaforesaid test methods.

Example 6

A solution was prepared by mixing 50 parts of a polydimethylsiloxane ofthe following formula, herein after referred to as “polydimethylsiloxaneA6”, having a vinyl group in an amount of 0.007 mole/100 g and aviscosity in a 30% solution in toluene of 21,000 mPa·s

wherein x=7,560, y=38 and z=0, 83.3 parts of a 60% solution of thepolysiloxane B in toluene, and 33.4 parts of toluene, to which 0.5 partof 28% solution of ammonium in water was added and mixed at roomtemperature for 6 hours.

Then, the mixture was heated under reflux for 4 hours to removed ammoniagas and water. After cooled, fresh toluene was added to compensate fordistilled off toluene. To 100 parts of the reaction product thusobtained, 0.40 parts of the polyorganosiloxane C1, and 0.20 part ofethynylcyclohexanol were added and mixed.

To 100 parts of the mixture obtained containing about 60 wt % ofsiloxanes, 50 parts of toluene, and 0.5 part of the platinum complexsolution were further added to prepare a silicone composition containingabout 40 wt % of siloxanes. The silicone composition for pressuresensitive adhesive thus obtained was evaluated according to theaforesaid test methods.

Example 7

A solution was prepared by mixing 40 parts of a polydimethylsiloxane ofthe following formula, herein after referred to as “polydimethylsiloxaneA7”, having a vinyl group in an amount of 0.02 mole/100 g and aviscosity in a 30% solution in toluene of 20,000 mPa·s,

wherein x=7,290, y=110 and z=0, 100 parts of a 60% solution of thepolysiloxane B in toluene, and 26.7 parts of toluene, to which 0.5 partof 28% solution of ammonium in water was added and mixed at roomtemperature for 6 hours.

Then, the mixture was heated under reflux for 4 hours to removed ammoniagas and water. After cooled, fresh toluene was added to compensate fordistilled off toluene. To 100 parts of the reaction product thusobtained, 0.62 part of the polyorganosiloxane C1, and 0.20 part ofethynylcyclohexanol were added and mixed.

To 100 parts of the mixture obtained containing about 60 wt % ofsiloxanes, 50 parts of toluene, and 0.5 part of the platinum complexsolution were further added to prepare a silicone composition containingabout 40 wt % of siloxanes. The silicone composition for pressuresensitive adhesive thus obtained was evaluated according to theaforesaid test methods.

Example 8

A solution was prepared by mixing 50 parts of a polydimethylsiloxane ofthe following formula, herein after referred to as “polydimethylsiloxaneA8”, having a vinyl group in an amount of 0.001 mole/100 g and aviscosity in a 30% solution in toluene of 24,000 mPa·s,

wherein x=8,300, y=4 and z=0, and 83.3 parts of a 60% solution of thepolysiloxane B in toluene, and 33.4 parts of toluene, to which 0.5 partof 28% solution of ammonium in water was added and mixed at roomtemperature for 6 hours.

Then, the mixture was heated under reflux for 4 hours to removed ammoniagas and water. After cooled, fresh toluene was added to compensate fordistilled off toluene. To 100 parts of the reaction product thusobtained, 0.19 part of the polyorganosiloxane C1, and 0.20 part ofethynylcyclohexanol were added and mixed.

To 100 parts of the mixture obtained containing about 60 wt % ofsiloxanes, 50 parts of toluene, and 0.5 part of the platinum complexsolution were further added to prepare a silicone composition containingabout 40 wt % of siloxanes. The silicone composition for pressuresensitive adhesive thus obtained was evaluated according to theaforesaid test methods.

Comparative Example 1

A solution was prepared by mixing 50 parts of a polydimethylsiloxane ofthe following formula, herein after referred to as “polydimethylsiloxaneA9”, having a vinyl group in an amount of 0.07 mole/100 g and aviscosity in a 30% solution in toluene of 15,000 mPa·s,

wherein x=6,070, y=330 and z=0, 83.3 parts of a 60% solution of thepolysiloxane B in toluene, and 33.4 parts of toluene, to which 0.5 partof 28% solution of ammonium in water was added and mixed at roomtemperature for 6 hours.

Then, the mixture was heated under reflux for 4 hours to removed ammoniagas and water. After cooled, fresh toluene was added to compensate fordistilled off toluene. To 100 parts of the reaction product thusobtained, 2.69 parts of the polyorganosiloxane C1, and 0.20 part ofethynylcyclohexanol were added and mixed.

To 100 parts of the mixture obtained containing about 60 wt % ofsiloxanes, 50 parts of toluene, and 0.5 part of the platinum complexsolution were further added to prepare a silicone composition containingabout 40 wt % of siloxanes. The silicone composition for pressuresensitive adhesive thus obtained was evaluated according to theaforesaid test methods.

Comparative Example 2

A solution was prepared by mixing 35 parts of a polydimethylsiloxane ofthe following formula, hereinafter referred to as “polydimethylsiloxaneA10”, having a vinyl group in an amount of 0.001 mole/100 g and aviscosity in a 30% solution in toluene of 20,000 mPa·s,

wherein x=7,400, y=4 and z=0, 108.3 parts of a 60% solution of thepolysiloxane B in toluene, and 23.4 parts of toluene, to which 0.5 partof 28% solution of ammonium in water was added and mixed at roomtemperature for 6 hours.

Then, the mixture was heated under reflux for 4 hours to removed ammoniagas and water. After cooled, fresh toluene was added to compensate fordistilled off toluene. To 100 parts of the reaction product thusobtained, 0.13 part of the polyorganosiloxane C1, and 0.20 part ofethynylcyclohexanol were added and mixed.

To 100 parts of the mixture obtained containing about 60 wt % ofsiloxanes, 50 parts of toluene, and 0.5 part of the platinum complexsolution were further added to prepare a silicone composition containingabout 40 wt % of siloxanes. The silicone composition for pressuresensitive adhesive thus obtained was evaluated according to theaforesaid test methods.

Comparative Example 3

A solution was prepared by mixing 70 parts of a polydimethylsiloxane ofthe following formula, hereinafter referred to as “polydimethylsiloxaneA11”, having a vinyl group in an amount of 0.0005 mole/100 g and aviscosity in a 30% solution in toluene of 16,000 mPa·s, 50 parts of a60% solution of the polysiloxane B in toluene,

wherein x=6,600, y=1 and z=0, 50 parts of a 60% solution of thepolysiloxane B in toluene, and 46.7 parts of toluene, to which 0.5 partof 28% solution of ammonium in water was added and mixed at roomtemperature for 6 hours.

Then, the mixture was heated under reflux for 4 hours to removed ammoniagas and water. After cooled, fresh toluene was added to compensate fordistilled off toluene. To 100 parts of the reaction product thusobtained, 0.20 part of the polyorganosiloxane C1, and 0.22 part ofethynylcyclohexanol were added and mixed.

To 100 parts of the mixture obtained containing about 60 wt % ofsiloxanes, 50 parts of toluene, and 0.5 part of the platinum complexsolution were further added to prepare a silicone composition containingabout 40 wt % of siloxanes. The silicone composition for pressuresensitive adhesive thus obtained was evaluated according to theaforesaid test methods.

Comparative Example 4

A solution was prepared by mixing 100 parts of a polydimethylsiloxane ofthe following formula, hereinafter referred to as “polydimethylsiloxaneA12”, having a vinyl group in an amount of 0.002 mole/100 g and aviscosity in a 30% solution in toluene of 3,500 mPa·s,

wherein x=3,400, y=3 and z=0, and 66.7 parts of toluene. To 100 parts ofthe solution, 0.38 part of the polyorganosiloxane C1, and 0.20 part ofethynylcyclohexanol were added and mixed.

To 100 parts of the mixture obtained containing about 60 wt % ofsiloxane, 50 parts of toluene, and 0.5 part of the platinum complexsolution were further added to prepare a silicone composition containingabout 40 wt % of siloxanes. The silicone composition for pressuresensitive adhesive thus obtained was evaluated according to theaforesaid test methods.

Comparative Example 5

Mixed were 50 parts of a polydimethylsiloxane of the following formula,hereinafter referred to as “polydimethylsiloxane A13”, having a vinylgroup in an amount of 0.063 mole/100 g and a viscosity of 60 mPa·s,

wherein x=40, y=0 and z=0, 83.3 parts of a 60% solution of thepolysiloxane B in toluene, and 4.85 parts of a polymethylhydrosiloxaneof the following formula, hereinafter referred to as“polymethylhydrosiloxane C2”, having SiH groups,

from which mixture toluene was removed by heating the mixture at atemperature of 90° C. and at a reduced pressure. After cooling themixture, 0.2 part of ethynylcyclohexanol, and 1.0 part of the solutionof a complex of platinum with a siloxane having a vinyl group in toluenein a concentration as platinum of 0.05 wt % were added to 100 parts ofthe mixture to prepare solvent-free composition, which was evaluatedaccording to the aforesaid test methods.

Comparative Example 6

A 30 wt % of solution of a commercially available two-pack type weakadhesive composition comprising an acrylic resin and an isocyanatehardener in toluene was prepared, which solution was evaluated accordingto the aforesaid test methods. The tests of bubble entrapment, holdingpower, peelability, and adhesion strength were performed on a filmprepared by applying the composition directly on a corona-treatedpolyethylene film having a thickness of 75 μm without the siliconeprimer treatment.

Table 1 shows test results of pressure sensitive adhesive films preparedfrom each composition prepared above.

TABLE 1 Vinyl Adhesion content of Holding to Mass ratio of (A) Corona-Primer- Adhesion power Bubble Peel- substrate (A)/(B) (mole/100 g)treated treated (N/10 mm) (mm) entrapment ability film Example 1-1 A1/B= 90/10 0.002 Yes Yes 0.03 0.01 A A A Ref. Ex.*¹ 1 A1/B = 90/10 0.002 NoNo — — — — C Ref. Ex. 2 A1/B = 90/10 0.002 Yes No — — — — B Example 1-2A1/B = 90/10 0.002 No Yes 0.03 0.01 A A A Example 2 A2/B = 70/30 0.002Yes Yes 0.20 0.01 A A A Example 3 A3/B = 70/30 0.002 Yes Yes 0.27 0.01 AA A Example 4 A4/B = 75/25 0.04 Yes Yes 0.01 0.01 A A A Example 5 A5/B =50/50 0.04 Yes Yes 0.02 0.01 A A A Example 6 A6/B = 50/50 0.007 Yes Yes0.45 0.01 A A A Example 7 A7/B = 40/60 0.02 Yes Yes 0.10 0.01 A A AExample 8 A8/B = 50/50 0.001 Yes Yes 1.1  0.02 A A A Comp. Ex.*² 1 A9/B= 50/50 0.07 Yes Yes 0.00 Slid off Not adhered — A Comp. Ex. 2 A10/B =35/65 0.001 Yes Yes 4.3  0.02 A C A Comp. Ex. 3 A11/B = 70/30 0.0005 YesYes Not hardened — — — — Comp. Ex. 4 A12/B = 100/0 0.002 Yes Yes 0.01Slid off A A A Comp. Ex. 5 A13/B = 35/65 0.04 Yes Yes 0.04 0.01 A A CComp. Ex. 6 Acrylic — Yes No 0.38 0.15 C C A *¹Referential Example*²Comparative Example

As shown in the Table 1, the present pressure sensitive adhesive filmswere applied on a glass without entrapping bubbles. The films hadadhesion strength suitable for use as a film for a flat panel display.

1. A method for protecting a surface of a flat panel display comprisinga step of: applying a pressure sensitive adhesive film comprising asubstrate film and a pressure sensitive adhesive layer formed on asurface of the substrate film, wherein said pressure sensitive adhesivelayer is prepared from a silicone composition comprising: (A) adiorganopolysiloxane, having at least two alkenyl groups per molecule,which diorganopolysiloxane contains alkenyl groups in an amount of from0.002 to 0.05 mole per 100 g of the diorganopolysiloxane (A); (B) apolyorganosiloxane comprising an R¹ ₃SiO_(0.5) unit and an SiO₂ unit ina molar ratio of the R¹ ₃SiO_(0.5) unit to the SiO₂ unit of from 0.6 to1.7, wherein R¹ is a monovalent hydrocarbon group having 1 to 10 carbonatoms; and (C) a polyorganosiloxane having an SiH bond contained saidcomposition in such an amount that a molar ratio of the SiH bond to thealkenyl group of the diorganopolysiloxane (A) ranges from 0.5 to 20,wherein in said composition a mass ratio of the diorganopolysiloxane (A)to the polyorganosiloxane (B) ranges from 95/5 to 55/45, and wherein theadhesive layer has an adhesion strength ranging from 0.01 to 0.5 N/10 mmmeasured according to the 180-degree peel test specified in the JapaneseIndustrial Standard Z 0237 on a film composed of a polyethyleneterephthalate film having a thickness of 25 μm and the adhesive layerhaving a thickness of 30 μm provided on the polyethylene terephthalatefilm to a surface of a flat panel display.
 2. The method according toclaim 1, wherein the flat panel display is a member selected from thegroup consisting of CRT displays, liquid crystal displays, plasmadisplays, organic electroluminescence displays, inorganicelectroluminescence displays, LED displays, surface-conductionelectron-emitter displays, and field emission displays.
 3. The methodaccording to claim 1, wherein said silicone composition furthercomprises 0 to 8.0 parts by mass, based on a total of (A) and (B) of 100parts by mass, of a retarder (D), 5 to 2,000 ppm, calculated asplatinum, based on a total of (A) and (B) of 100 parts by mass, of aplatinum catalyst (E), and 25 to 900 parts by mass, based on a total of(A) and (B) of 100 parts by mass, of an organic solvent (F).
 4. Themethod according to claim 1, wherein a mass ratio of thediorganopolysiloxane (A) to the polyorganosiloxane (B) is 55/45 and thealkenyl group is contained in an amount of from 0.005 to 0.05 mole per100 g of the diorganopolysiloxane (A).
 5. The method according to claim1, wherein a part or all of the components (A) and (B) are contained asa product prepared by reacting the part or all of the components (A) and(B) in the presence of a basic catalyst.
 6. The method according toclaim 1, wherein the alkenyl group of the diorganopolysiloxane (A) is avinyl group.
 7. The method according to claim 1, wherein thediorganopolysiloxane (A) is represented by the following formula:

wherein R² is a substituted or unsubstituted monovalent hydrocarbongroup which does not have an aliphatic unsaturated bond, R³ is anorganic group having an alkenyl group, “a” is an integer of from 0 to 2,“m” is an integer of 0 or larger, provided that “m” is 2 or larger when“a” is zero, “n” is an integer of 10 or larger, with a sum of “m” and“n” being such that the diorganopolysiloxane has a viscosity of 10 mPa·sor larger.
 8. The method according to claim 1, wherein said film has aprimer layer between the substrate film and the pressure sensitiveadhesive layer.
 9. The method according to claim 8, wherein a surface ofthe substrate film has been corona-treated and the primer layer isplaced on the corona-treated surface.
 10. The method according to claim1, wherein said silicone composition consists of the aforesaidcomponents (A), (B), and (C) and at least one component selected fromnon-reactive polyorganosiloxanes having no alkenyl group, antioxidants,photostabilizers, flame retardants, antistatic agents, dyes, andpigments.